Poststernotomy Mediastinitis Caused by Staphylococcus simulans: A Case Report Highlighting the Importance of Clinicomicrobiological Interpretation of Coagulase-Negative Staphylococci

Poststernotomy mediastinitis is a serious complication of cardiac surgery.Although coagulase-negative staphylococci can cause deep postoperative infections, their clinical significance may be difficult to establish because of their frequent presence as skin commensals.We report the case of a 71-year-old woman who developed fever, anterior chest pain, and purulent discharge from the sternal wound on the fifth postoperative day after triple coronary artery bypass grafting.Chest computed tomography revealed a retrosternal collection consistent with poststernotomy mediastinitis.Surgical re-exploration with drainage, debridement, and collection of deep microbiological specimens was performed.Direct examination revealed numerous neutrophils and Gram-positive cocci arranged in clusters and tetrads.A pure culture yielded Staphylococcus simulans, identified by VITEK® MS PRIME matrix-assisted laser desorption/ionization timeof-flight mass spectrometry (bioMérieux, Marcy-l'Étoile, France).The isolate was resistant to methicillin, fluoroquinolones, aminoglycosides, and rifampicin but remained susceptible to vancomycin.Surgical debridement combined with six weeks of intravenous vancomycin resulted in a favorable clinical and biological outcome, with no recurrence at three months.This case emphasizes that the recovery of a coagulase-negative Staphylococcus from a deep specimen should not automatically be interpreted as contamination.Its etiological significance should instead be determined through the concordance of clinical, radiological, surgical, and microbiological findings.